This invention relates to a television synchronizing signal processing circuit in a still video floppy system, etc., which is used to read a video signal from a disc memory and display it on a CRT screen.
A 1/2 interlace scanning is adopted in an ordinary TV standard system. In an NTSC system, for example, the horizontal scanning line of one field is 262.5 H (1H: the period of one horizontal synchronizing signal) with 1 frame =2 field =525 H. To reproduce data from a rotation disc of an electronic still camera, which is recorded at a rate of one field (=262.5 H) per rotation, the horizontal synchronizing pulse is displaced by a time 0.5 H (i.e. one half of the horizontal synchronizing pulse) at a junction (a starting point or an ending point) between recording tracks. In this case, an image distortion occurs on the CRT screen in an ordinary TV receiver, making it impossible to provide an accurate image display. It is therefore required to delay reproduced signal read out from the disc for every other field by 0.5 H to obtain a continuous reproduced horizontal sync signal.
If, on the other hand, no delay of 0.5 H is given to the vertical synchronization signal, a standard 1/2 interlace scanning will be performed. However, the resultant still image has the following drawbacks. Where one scanning line corresponding to a white color is generated between two horizontal scanning lines, each corresponding to a black color or a given scanning line is located at a boundary between the white and black colors, a non-delayed raster and 0.5 H-delayed raster (i.e. a raster vertically displaced by a spacing corresponding to one scanning line) are alternately displayed for each field and the display raster is moved up and down for each field by a spacing corresponding to one scanning line, resulting in an unstable still image.
In order to eliminate the drawback, the phase of the vertical synchronizing signal has to be controlled, without performing the 1/2 interlace so that the aforementioned rasters assume substantially the same positions for every field.